This invention relates to a logic tracing apparatus and particularly to a logic tracing apparatus for obtaining a history of the hardware status concerning an error when the error is detected during the diagnosis of a data processor.
When the data processor (including any type of logic devices based on program control) is diagnosed, a test program is generally run. In order to analyze the error detected by the diagnosis, it is necessary to take out the history of the hardware status just before the error detection. To do this, a logic tracing apparatus is connected to the data processor so that hardware status information to be inspected is written sequentially at constant time intervals in a memory within the logic tracing apparatus.
In the prior art, the writing of the hardware status information is stopped by a stop signal generated when an error is detected in the data processor. However, when an error occurs during the running of a test program, a certain time elapses until the error is detected by a result comparison routine of the test program. Thus, unless the memory within the logic tracing apparatus has a considerably large capacity, the desired pieces of recorded information may be lost.
In the conventional method, the write operation is necessarily restarted by a start signal which is always generated when no error is detected by the result comparison routine of the test program. In this case, when only one test program is used, there is particularly no problem. However, where two or more test programs are used for diagnosis, the stop signal generated when an error is detected by the result comparison routine of one of the test programs stops the writing operation of the logic tracing apparatus, but the write operation is restarted by the start signal which may be generated by the run of another test program, thereby erasing the recorded history.